This invention relates generally to electronically controlled fuel injection systems and, more particularly, to a method and apparatus for accurately delivering multiple separate fuel injections to the cylinders of an internal combustion engine during a fuel injection event based upon engine operating conditions when the engine experiences an acceleration or when two fuel injection events are separated by a short period of time.
Electronically controlled direct fuel injection devices such as electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder in response to an electronic fuel injection signal received from an electronic fuel injection control device (controller) or system. These signals define waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders.
Emission regulations pertaining to engine exhaust emissions are becoming more restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, the release of particulates, and the release of nitrogen oxides (NOx). Tailoring the electronic fuel injection current signal waveform and the resulting number of injections and the injection rate of fuel to a combustion chamber during a combustion cycle of the cylinder, as well as the quantity and timing of such fuel injections, is one way to improve emissions and meet higher emissions standards. As a result, many different multiple fuel injection techniques, wherein the electronic fuel injection signal waveform comprises a plurality of distinct fuel injection signals, have been utilized to modify the bum characteristics of the combustion process in an attempt to reduce emission and noise levels. Some techniques involve the use of multiple fuel injections into a single cylinder during a single engine operating cycle, and typically involve splitting the total fuel delivery to the cylinder during a particular engine operating cycle into separate fuel injections. Such injections may include a pilot injection, a main injection, and an anchor injection, where three injections of fuel (a three shot injection) are desired to achieve a desired performance. Each of these fuel injections may also be referred to generally as a xe2x80x9cshotxe2x80x9d. The xe2x80x9ccontrol current signalxe2x80x9d (electronic fuel injection current signal), also may be referred to simply as a xe2x80x9cfuel injection signalxe2x80x9d to a fuel injector indicative of an injection or delivery of fuel to the engine.
At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine performance and emissions control. For example, any of a variety of multiple fuel injection techniques may be utilized at certain steady-state engine operating conditions, including low engine speed and low engine load, while other techniques may be utilized at different engine operating conditions requiring high speed or torque. In the past, the controllability of a multiple fuel injection or split injection event has been somewhat restricted by mechanical and other limitations associated with the particular types of injectors utilized. Even with more advanced electronically controlled injectors, during certain engine operating conditions, it is sometimes difficult to accurately control fuel delivery.
As used throughout this disclosure, an xe2x80x9cinjection eventxe2x80x9d is defined as the activity, including the injection of one or more shots, that occur in a particular cylinder or combustion chamber during one operating or combustion cycle of the engine (a xe2x80x9ccylinder cyclexe2x80x9d). For example, one cycle of a four stroke engine for a particular cylinder includes an intake stroke, compression stroke, expansion stroke, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. As used in the art, and throughout this disclosure, an xe2x80x9cengine operating cyclexe2x80x9d includes the individual cylinder cycles for the cylinders included therein. For example, an engine operating cycle for a six cylinder engine will include six individual cylinder cycles, one for each of the cylinders of the engine (with each cylinder cycle having four strokes, for a total of 24 strokes). Generally, the cylinder cycles overlap, so that the beginning of the next successive cylinder cycle of a particular cylinder might begin prior to the completion of the beginning of the next engine operating cycle.
U.S. Pat. No. 5,901,682 to McGee et al., which is commonly assigned to the Assignee hereof, describes a direct fuel injection compression ignition engine and a process for transitioning between different engine operating modes. The ""682 patent describes calculating a weighted average transition fuel rate for smoothly transitioning between operating modes. The ""682 patent does not, however, describe transitioning between a mode having a first characteristic injection shape, especially a split injection configuration or mode, and a mode having a second characteristic injection shape, especially a boot injection configuration or mode.
Desired engine performance is not always achieved at all engine speeds and engine load conditions using previously known fuel injection strategies where, based upon engine operating conditions, the injection timing, number and duration of shots, fuel flow rate and the injected fuel volume are determined in order to reduce emissions and improve fuel consumption. As a result, problems such as injecting fuel too rapidly within a given injection event and/or allowing fuel to be injected beyond a desired stopping point can adversely affect system stability, emission outputs and fuel economy.
In a fuel control system for an internal combustion engine in which one or multiple shots may be used in a given injection event and different injection signal waveforms are achievable, it is desirable to control and deliver any number of separate fuel injection shots to a particular cylinder so as to minimize emissions and fuel consumption based upon the operating conditions of the engine at that particular point in time, e.g. changes in speed, load, or ambient conditions. Such strategies may include splitting the fuel injection into two or more separate fuel shots during a particular injection event, advancing the pilot shot during the injection event, and adjusting the timing between the various multiple fuel injection shots in order to achieve desired emissions and desired fuel consumption. In some situations, it is also desirable to rate shape the front end of the fuel delivery to the cylinder to control the burn characteristics of the particular fuel being utilized. However, in some situations the particular shot duration or the fuel quantity for a given shot may be so small that it is not practical to inject the particular shot.
By way of example, during certain acceleration events, not all of the fuel delivered to the engine in the distinct fuel shots of a multi-shot fuel injection event is combusted for a variety of reasons. In one such event where a turbo charger is used, during an acceleration event the air mass delivered to the engine is lower because the turbo charger device associated with the engine has to spin up to deliver a greater quantity of air corresponding to the increase in the fuel. When a rich fuel mixture is introduced into the cylinder, more fuel is likely to contact the cylinder walls than with a comparatively leaner fuel mixture. Because a cylinder""s walls are typically cooler in comparison to the interior of the cylinder, the fuel does not combust but instead mixes with the cylinder wall lubricating oil. This fuel deteriorates the lubricating quality of the engine oil and adversely impacts the fuel efficiency of the engine. Furthermore, such uncombusted fuel may be emitted in the form of hydrocarbons, which are a pollutant and therefore an undesirable component of an engine""s emissions.
Further during an acceleration event, the time window used for fuel injection events may decrease. Thus, it becomes more difficult to inject multiple shots into a shrinking time window for a cylinder as engine speed increases. Rapidly changing engine speed can cause timing errors for all shots and in particular for shots that are placed at a particular piston position (crank angle). However, this is especially applicable to the anchor shot since it occurs a time delay after the main shot. As a result, the time interval between shots, or the time difference between the end of one fuel shot in a particular fuel injection event and the beginning of a subsequent fuel shot in the same fuel injection event, decreases. Therefore, it becomes increasingly important to deliver the individual fuel shots accurately as the timing between fuel shots becomes shorter.
Further, because the injectors in a given engine may have widely varying performance characteristics, and the quantity of fuel injected may vary despite commands of the same time duration, there is a need to provide stability to the operation of the injectors, particularly during periods where the mode of injector operation must transition from one mode to another mode.
Additional problems may be observed where the transition is from a one mode used for low speed operating conditions, and another mode, used for higher speed operating conditions. For example, xe2x80x9cgas ingestionxe2x80x9d by the fuel injector may occur when the pressure in the cylinder or combustion chamber is greater than the pressure in the fuel injector tip, e.g., during combustion of the main shot when an injector attempts to inject fuel into the cylinder. When an injector attempts to inject fuel under these conditions, hot gasses are blown into the injector from the cylinder, causing a void in fuel flow through the injector. Then, when the injector attempts to force fuel out of the injector nozzle (inject fuel), the injector tip will be forced into the injector tip check, damaging the injector. Transitioning between modes can cause gas ingestion.
Moreover, the changing engine speed under acceleration conditions corresponds to a change in the crank angle (timing) for injecting the particular fuel shot. Therefore, the desired angle previously determined for the injection of each fuel shot in each fuel injection event (prior to the acceleration conditions) might be slightly offset from the desired angle of injection after acceleration conditions. Such a situation is not desirable because offset fuel injection shots may detrimentally impact the engine""s performance, efficiency, and emissions.
It is therefore desirable to provide an apparatus and method to control the delivery of fuel to an engine to control emissions during acceleration and deceleration. Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, an apparatus and method are disclosed for controlling a fuel injection system, which is adapted to operate in at least a split injection mode and a boot injection mode, and which comprises steps or means for determining whether an acceleration condition exists, and on the basis of such determination, rapidly changing from a split injection mode to a boot injection mode.
In another aspect of the present invention A fuel injection control system and/or a controller is operative to identify an acceleration condition on the basis of at least one sensed acceleration-related engine operating condition, and to rapidly change the fuel injection mode for at least one fuel injector from the split fuel injection mode to the boot fuel injection mode. The fuel injection control system and/or a controller is also operable to determine a rail pressure, whether the rail pressure is within a predetermined limit, and on that basis, to modify at least one of a main fuel injection signal timing and an anchor fuel injection signal timing such that a resulting multiple fuel injection has a boot injection shape.
Another aspect of the present invention describes a method and apparatus for controlling a fuel injection system to partition fuel output delivery to a plurality of direct fuel injection devices which transitions fuel delivery between the desired first injection characteristic shape and the desired second injection characteristic shape based on engine operating parameters.